Shares in Imperial Brands have dived 10% after the tobacco giant warned that the crackdown on flavoured e-cigarettes in the US would hit its sales.
The UK firm has invested heavily in vaping products, which many believe are safer than tobacco.
But it warned that demand in the US had fallen sharply since Donald Trump vowed to ban flavoured varieties this month.
A rising number of wholesalers and retailers are “not ordering or allowing promotion” of the products, it warned.
The Trump administration plans to pull fruit flavoured e-cigarettes from the US market, unless approved by the Food and Drug Administration, in an attempt to make them less attractive to young consumers.
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It follows a backlash against vaping firms, such as fast-growing Juul, whose products are widely used by US teenagers.
US regulators are also examining hundreds of cases of people who have fallen ill from what appears to be a vaping-related lung disease. There have been six deaths and 450 reported cases of lung illness across 33 states.
Imperial Brands, which is the fourth biggest cigarette firm in the world, has seen strong growth in sales of flavoured e-cigarettes such as its product Blu.
But it said it now expected growth in its cigarette alternatives division to be lower than expected this year, at 50%.
Along with tougher trading conditions in Africa, Asia and Australasia, it said it now saw group revenues growing by 2%, down from a previously forecast 4%.
Vaping devices, which vaporise liquid containing nicotine, have suffered a number of regulatory crackdowns globally.
Last week, India joined other the likes of Brazil and Singapore in banning the sale of e-cigarettes, as it warned of an “epidemic” among young people.
It has come as a blow to tobacco companies, which have been pumping investment into vaping and tobacco heating products.
While these products still account for only a fraction of revenue at the biggest firms, demand for them is growing fast.
Despite the regulatory pressure, many countries including the UK have no plans to curb e-cigarette use.
Last week, Public Health England issued a statement saying that “vaping isn’t completely risk free, but is far less harmful than smoking tobacco. There is no situation where it would be better for your health to continue smoking rather than switching completely to vaping,” it said.